1.3 FCAW — Flux-Cored Arc Welding

Flux-Cored Arc Welding (FCAW)

Flux-Cored Arc Welding (FCAW) is the hybrid that marries GMAW's continuous feed to SMAW's internal flux. The electrode is a tubular wire — a thin metal sheath wrapped around a powdered flux core — fed on a constant-voltage (CV) source. As the wire melts, the flux performs the same jobs as a stick coating: it forms a slag, releases shielding gas, deoxidizes, and can add alloys. The result is high deposition with the deep penetration and forgiving nature welders associate with stick. FCAW is the dominant process in structural steel erection, shipbuilding, and heavy fabrication.

Two Variants

FCAW-S is the go-to for field welding because there are no cylinders to haul and no wind screens to rig; the flux decomposition alone shields the pool, holding up in winds of 35 mph or more. AWS D1.1 prequalifies FCAW for structural work, and FCAW-S erects most steel bridges and buildings.

Why FCAW Wins on Productivity

• Deposition rate 8–25+ lbs/hr — far above SMAW, rivaling or beating GMAW
• All-position capability with the right wire (e.g., E71T-1)
• Deep penetration on thick members
• Slag coverage that shapes the bead and slows cooling
• High duty cycle — continuous wire means fewer stops

The trade-off is that FCAW combines the productivity of a wire process with the slag-removal burden of a flux process: every pass leaves a slag layer that must be chipped before the next, and trapped slag at the toe or between passes is the most common FCAW discontinuity an inspector finds. Gas-shielded FCAW also depends on shielding gas coverage just like GMAW, so wind, low flow, or a clogged nozzle produces porosity.

Wire Classification (AWS A5.20)

The carbon-steel FCAW spec is AWS A5.20. Decoding the designation is a reliable Part A question.

Example: E71T-1C

Self-Shielded vs. Gas-Shielded — Inspector's View

A self-shielded gotcha the CWI must watch: many FCAW-S wires contain aluminum as a denitrider, and some T-4/T-7/T-8 wires have impact-toughness or amperage restrictions — using the wrong wire or excess heat input can drop Charpy values below code. Storage matters too: tubular wire can wick moisture into its core, so opened spools are kept dry to avoid hydrogen pickup and porosity. Worked heat input: 300 A, 26 V, 12 ipm → (26 × 300 × 60)/12 = 39,000 J/in (39 kJ/in).

The usability digit after the "T" tells the inspector a great deal about how a wire runs and what it is approved for. T-1 wires give a smooth spray-like arc and good all-position performance on gas; T-5 wires use basic (lime) slag for superior toughness and crack resistance but run with a globular, less-forgiving arc; T-8 is the all-position self-shielded standard for field structural work; and T-4 / T-7 / T-11 are self-shielded wires tuned for high deposition or fast-fill. The single-pass-only wires (such as some T-3 and T-10 designs) must never be used for multipass welds, a restriction that appears in WPS reviews.

, E71T-1CJ) signals improved low-temperature impact toughness — important for bridges and cold-service structures. Reviewing these designators against the joint's service requirements is a routine CWI document-control task before welding begins.

Exam trap: The "T" means tubular, not tensile. FCAW-S needs no external gas; FCAW-G does.

A5.20 Usability Designators and Field Discontinuities

The "T" usability digits in AWS A5.20 are not arbitrary — each one tells the inspector how the wire transfers metal, what polarity it runs, and whether it is single- or multipass rated. A quick reference the CWI should carry into a WPS review:

Polarity is part of the operating designator: most gas-shielded T-1 wires run DCEP (reverse), while several self-shielded wires such as T-8 run DCEN (straight) — using the wrong polarity degrades the arc and toughness. Single-pass-only designators (some T-3, T-10) must never appear on a multipass WPS, because their deoxidizer balance is tuned for one-pass dilution and will overalloy on rebuild.

Self-Shielded vs. Gas-Shielded Metallurgy

FCAW-S wires shield the pool by decomposing flux that releases CO and CO₂ and adds strong denitriders — chiefly aluminum, sometimes with magnesium or titanium — to tie up the atmospheric nitrogen that the open arc would otherwise dissolve. That aluminum is why many self-shielded wires carry amperage and CTWD (electrode-extension) limits: run too hot or too long a stickout and nitrogen pickup, aluminum carryover, and reduced impact toughness follow.

Gas-shielded FCAW-G has no such denitrider load because the external CO₂ or Ar/CO₂ blanket excludes air, so it generally gives smoother beads and more consistent Charpy values in the shop.

Common FCAW Discontinuities

• Interpass slag inclusions — the signature FCAW finding; every pass leaves slag that must be fully removed before the next, and trapped slag at the toe or in a sharp bead valley is the most frequent reject.
• Porosity — FCAW-G loses its gas shield in wind, low flow, or a clogged nozzle; tubular wire that has wicked moisture into its core releases hydrogen and pores either variant.
• Worm-tracking (surface porosity) — long gas channels on the bead face from moisture or excessive voltage.
• Lack of fusion — cold-lap from too low voltage/amperage or fast travel on thick sections.

Storing opened spools dry and verifying gas flow and CTWD against the WPS heads off most of these.